1. Field of the Invention
This invention relates to the preparation of alkylpolyglycosides by the reaction of a saccharide and an alcohol in the presence of an acid catalyst, and particularly to an improvement in the process to inhibit condenser fouling during the processing either in the removal of water from the reactor to promote completion of the reaction or in subsequent processing of the alkylpolyglycoside reaction product stream wherein the stream is heated at elevated temperatures and vacuum, i.e. evaporation or distillation to remove excess alcohol and any residual water remaining in the stream after leaving the reactor (e.g. via steam ejectors).
2. Statement of Related Art
Alkyl glycosides are conveniently prepared by reacting an alcohol of the type and chain length which is desired to form the "alkyl" portion of the glycoside of interest with a saccharide reactant (e.g., a monosaccharide such as glucose, xylose, arabinose, galactose, fructose, etc., or a polysaccharide such as starch, hemicellulose, lactose, maltose, melibiose, etc.) or with a glycoside starting material wherein the aglycone portion thereof is different from the alkyl substituent desired for the ultimate alkyl glycoside product of interest. Typically, such reaction is conducted at an elevated temperature and in the presence of an acid catalyst. Various alkyl glycoside products and processes for making same are disclosed in a variety of representative patents.
U.S. Pat. No. 4,987,225 contains an extensive listing of processes for preparing alkylpolyglycosides, the description of which is hereby incorporated by reference. Included therein is U.S. Pat. No. 4,393,203 to Mao et al (issued Jul. 12, 1983) which includes the step of removal of the excess alcohol in a thin film evaporator. U.S. Pat. No. 5,079,350 further describes a method for removing unreacted alcohol from the glycoside surfactant product by contacting the alkylpolyglycoside and alcohol mixture with a spraying stream of inert gas under reduced pressure in a thin film evaporator maintained at a temperature in the range of about 140.degree. C. to about 200.degree. C. The process is described as substantially removing all of the unreacted alcohol and odor from the glycoside product.
In the process, condensers are employed at the reactor stage and at the removal of excess alcohol stage. In the condenser a gel-like emulsion frequently forms presenting condenser plugging problems, the severity of which varies with the alcohol source, particularly those containing a long carbon chain, i.e., 10 or more carbons. It was demonstrated in the laboratory that the gel-like emulsion which typically forms is an emulsion of only the alcohol components and water, in which a film of alcohol surrounds droplets of water. The gel formed in the laboratory only contains alcohol and water. In commercial larger scale operations, the possibility exists that during upset conditions, for example entrainment, a more complex gel structure may be present which may include some alkylpolyglycoside itself and the saccharide i.e. glucose.